docs: def spkpvn(handle, descr, et):
      """
      For a specified SPK segment and time, return the state (position and
      velocity) of the segment's target body relative to its center of
      motion.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/spkpvn_c.html
  
      :param handle: File handle.
      :type handle: int
      :param descr: Segment descriptor.
      :type descr: 5-Element Array of floats
      :param et: Evaluation epoch.
      :type et: float
      :return:
              Segment reference frame ID code,
              Output state vector,
              Center of state.
      :rtype: tuple
      """
      handle = ctypes.c_int(handle)
      descr = stypes.toDoubleVector(descr)
      et = ctypes.c_double(et)
      ref = ctypes.c_int()
      state = stypes.emptyDoubleVector(6)
      center = ctypes.c_int()
      libspice.spkpvn_c(handle, descr, et, ctypes.byref(ref), state,
                        ctypes.byref(center))
      return ref.value, stypes.cVectorToPython(state), center.value